Electroform, methods of making electroforms, and products made from electroforms

ABSTRACT

In one embodiment, a method for making an electroform, comprises passivating a sub-master to form a passivation layer. The passivation comprises contacting at least a surface of the sub-master with a solution comprising an oxidizing agent and applying an anodic current to the sub-master. The surface of the sub-master can be plated with a metal to form a metal layer. The metal layer can be removed to form the electroform.

BACKGROUND

This disclosure generally relates to electroforming and methods forforming an electroform.

Electroforming involves an electrochemical process that uses an anode(which may supply metal for deposition), an electrolyte, and a substrate(which acts as a cathode). An electrical current to the anode andcathode is controlled to manage the deposition of the metal onto thesubstrate to create a metal replica of various shapes and textures. Inanother example, electroforms can be made from a complex micromachinedmaster. The replicas (or micromachined master) can be used tomass-produce plastic articles with precise microstructure usingprocesses such as printing, embossing, and casting. For example, thesereplicas can be employed in the production of data storage media such asCDs, DVDs, and the like.

In backlight computer displays or other display systems, optical filmsare often used to direct light. For example, in backlight displays,light management films use prismatic structures (often referred to asmicrostructure) to direct light along a viewing axis (i.e., an axissubstantially normal to the display). Directing the light enhances thebrightness of the display viewed by a user and allows the system toconsume less power in creating a desired level of on-axis illumination.Films for turning or directing light can also be used in a wide range ofother optical designs, such as for projection displays, traffic signals,and illuminated signs. The prismatic structures are generally formed ina display film by replicating a metal tool, mold, or electroform havingprismatic structures disposed thereon, via processes such as stamping,molding, embossing, or UV-curing. It is generally desirable for thedisplay film and the mold to be free from defects so as to facilitate auniform luminance of light. Since such structures serve to stronglyenhance the brightness of a display, any defects, even if they are small(on the order of 10 microns), can result in either a very bright or verydark spot on the display, which is undesirable. The mold and the displayfilms are therefore inspected to eliminate defects.

Molds such as, for example, electroforms are generally used formanufacturing light management films such as prism sheets for use inliquid crystalline displays. In general, such light management filmshave at least one microstructured surface that refracts light in aspecific way to enhance the light output of the display. Since thesefilms serve an optical function, the surface features must be of highquality with no roughness or other defects. This microstructure is firstgenerated on a master, (e.g., a silicon wafer, glass plate, metal drum,or the such) and is created by one of a variety of processes such asphotolithography, etching, ruling, diamond turning, or others. Sincethis master tends to be expensive to produce and fragile in nature,tooling or molds are typically reproduced off of this master, which inturn serve as the molds from which plastic microstructured films aremass-produced. These tools can be metal copies grown via electroformingprocesses, or plastic copies formed via molding-type processes. Toolscopied directly from the master are called 1^(st)-generation(sub-master), copies of these tools are called 2^(nd)-generation(sub-master), etc. In general, multiple copies can be made of every toolmade at any generation, leading to a geometric growth in number of toolswith each generation—i.e. a “tooling tree” is produced. Each generationis an inverted image of the previous generation. If the desired finalproduct is a “positive” geometry, then any generation of tooling that isa negative can be used as a mass-production replication tool. If themaster is manufactured as a negative, then any even-generation mold canbe used for mass-production.

One difficulty always present when a manufacturing process, such as theoptical display film manufacturing process, uses a component orsubprocess in a subsequent step of the process is the systemic defect.If a major component, such as a shim tool or a master tool, isdefective, then every subsequent mold and film replicated from thosecomponents will be defective. In prior attempts to alleviate thisproblem, the optical display film manufacturing process has beenseparated into three semi-independent manufacturing processes, themaster tool, the shim tool and the display film manufacturing processes.Each primary manufacturing process has had an independent inspection anddefect correction process that identifies a defective component orproduct at that particular step in the process and then removes it fromthe process chain. These processes are intended to prevent a defectivemaster tool from being made into a defective shim tool, a defective shimtool from being made into defective film samples, and defective filmsamples from being sold.

Depending upon the size of the replica, the size, geometry, and amountof features to be replicated, and the materials of the master andsub-master, the degree of successful replication can vary greatly. Thereis a constant need to make the electroplating process more efficient(e.g., reduce the plating time), and more effective (e.g., improve theaccuracy of the replication, enhance the separation of sub-master frommaster, and reduce the amount of yield loss). These needs are especiallydifficult when the articles made from the electroform serve an opticalfunction, making tolerances critical and very small defectsunacceptable.

BRIEF SUMMARY

Disclosed herein are methods of making electroforms, electroforms madetherefrom, and products made from the electroforms.

In one embodiment, a method for making an electroform, comprisespassivating a sub-master to form a passivation layer. The passivationcomprises contacting at least a surface of the sub-master with asolution comprising an oxidizing agent and applying an anodic current tothe sub-master. The surface of the sub-master can be plated with a metalto form a metal layer. The metal layer can be removed to form theelectroform.

In another embodiment, the method for making an electroform cancomprise: contacting at least a surface of a sub-master with a solutioncomprising an alkaline metal hydroxide, wherein the surface comprisesfeatures to be replicated, and wherein the sub-master comprises nickel,applying an anodic current of about 1 ASF to about 40 ASF to thesub-master to form a passivation layer having a thickness of about 10 Åto about 500 Å, plating the surface of the sub-master with a metal toform a metal layer, and removing the metal layer to form theelectroform.

The above described and other features are exemplified by the followingfigure and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Refer now to the figures, which are exemplary, not limiting, and whereinlike numbers are numbered alike.

FIG. 1 is one embodiment of an electroforming process map.

FIG. 2 is a cross sectional view of a backlight display device.

FIG. 3 is a perspective view of an optical substrate comprising asurface characterized by a cross section of a prism having a curvedsidewall or facet.

FIG. 4 is a first cross sectional view of an optical substratecomprising a surface characterized by a cross section of a prism havinga curved sidewall or facet.

FIG. 5 is a second cross sectional view of an optical substratecomprising a surface characterized by a cross section of a prism havinga curved sidewall or facet.

FIG. 6 is a cross sectional view of a compound angle prism and of thegeometric parameters of the curved sidewall or facet of FIGS. 4 and 5 asdescribed by a segment of a polynomial function.

DETAILED DESCRIPTION

Ranges disclosed herein are inclusive and combinable (e.g., ranges of“up to about 25 wt %, or, more specifically, about 5 wt % to about 20 wt%”, is inclusive of the endpoints and all intermediate values of theranges of “about 5 wt % to about 25 wt %,” etc). Furthermore, the terms“first,” “second,” and the like, herein do not denote any order,quantity, or importance, but rather are used to distinguish one elementfrom another, and the terms “a” and “an” herein do not denote alimitation of quantity, but rather denote the presence of at least oneof the referenced item. The modifier “about” used in connection with aquantity is inclusive of the stated value and has the meaning dictatedby the context, (e.g., includes the degree of error associated withmeasurement of the particular quantity). The suffix “(s)” as used hereinis intended to include both the singular and the plural of the term thatit modifies, thereby including one or more of that term (e.g., thecolorant(s) includes one or more colorants).

FIG. 1 is a process map of one embodiment of an electroforming processfor making a sub-master and a 2^(nd) generation sub-master. The processcomprises forming a master drum having a pattern disposed in an externalsurface thereof. The pattern can be produced in various fashions, e.g.,photolithography, machining, etching, cutting, milling, scribing, amongother techniques. The master can be cleaned, e.g., washed with organicsolvents, water, acid, and/or base. To enable the removal of theelectrodeposited layer from the master, a release point can be formedand the drum can be passivated. The release point can be an area of themaster that is masked, such as with tape, to prevent metal deposition onthat area. The area is chosen to be outside of the pattern, and has alength to facilitate removal of the layer from the drum. For example,the tape can be disposed longitudinally across the master such that,once the layer has been disposed on the master, the tape can be removed,exposing an edge of the sub-master. The sub-master can then be removedby peeling it from around the drum. It is desirable to uniformly removethe sub-master from the drum without twisting or torquing thesub-master. Twisting, torquing, and other non-uniform removal can damagethe pattern on the surface of the sub-master and potentially even damagethe surface of the master.

To further facilitate the separation, the surface of the master can bepassivated which helps to prevent the replica (i.e., sub-master) fromadhering to the surface of the master. Possible passivation techniquesinclude the formation of a separation layer (such as an oxide and/orhydroxide layer) over the master surface, electrostatic cleaning, and/orby chemical passivation techniques. Formation of a separation layer cancomprise an electrolytic oxidation process wherein the electrolyticcurrent and voltage are applied to form a controlled thicknessseparation layer. Chemical passivation can comprise immersing the mastersurface in a solution for a controlled period of time. The particularsolution is dependent upon the master composition. Some possiblesolutions include alkali metal hydroxide solutions, chromate (such aspotassium dichromate), among others.

For example, the surface of the master can optionally be rinsed withSimple Green solution (commercially available from Sunshine Makers,Inc., located in Huntington Beach, Calif.) and then sprayed with asaponin solution to promote wetting of the surface. A potassiumdichromate solution (e.g., about 5 grams per liter (g/l)) can be appliedto the surface of the master (e.g., poured over the surface). Thepotassium dichromate is then rinsed from the master surface to form apassivated master. Optionally, the saponin and potassium dichromateapplications can be repeated as desired.

The passivated master can then be plated in various processes, includingan electroforming process. The electroforming process can be performedin an electroforming tank where the outer surface of the masterfunctions as the cathode through electrical contacts. The anode can beconstructed from various metals, including the metal to be depositedduring metallization. For example, a nickel anode or nickel alloy can beused if nickel is the desired metal in the metallization process. Forexample, the passivated master can be placed into an electroformingsolution and optionally rotated (e.g., up to about 10 revolutions perminute (rpm) or so) to more uniformly deposit the metal. A rectifier inelectrical communication with the anode and cathode can be maintainedconstant during this process or it can be adjusted. The electroformingcan be accomplished in up to about 24 hours.

The solution in the electroforming tank can be an aqueous solutioncomprising a surfactant agent, a pH of less than or equal to about 6,and optionally a hardening agent. The solution will further comprise themetal(s) to be deposited. One embodiment of a solution can compriseabout 60 grams per liter (g/l) to about 100 g/l of metal sulfamate(e.g., the metal to be deposited), sufficient acid to attain a pH ofless than or equal to about 6, a sufficient amount of surfactant agentto affect wetting of the metallic surface to be coated, and optionally ahardening agent, e.g., to control stress in the deposit. For example,the solution can comprise about 70 g/l to about 90 g/l nickel sulfamate,about 25 g/l to about 35 g/l boric acid, and sufficient sulfamic acid toattain a pH of about 2 to about 5.0.

When a current is applied to the system, the anodic metal oxidizes toform metal ions which then flow to the cathode (the outer surface of thepassivated master) and deposit thereon. The cathode then reduces themetal ion into elemental metal. The following shows the reactions at theanode and cathode for nickel:anode: Ni⁰−2e ⁻→Ni²⁺cathode: Ni²⁺+2e ⁻→NiElectroforming of other metals also go through similar reactions at theanode and cathode. Some of the possible metals for the electroformingprocess include, but are not limited to, nickel (Ni), cobalt (Co),copper (Cu), silver (Ag), iron (Fe), aluminum (Al), titanium (Ti),iridium (Ir), gold (Au), chromium (Cr), beryllium (Be), tungsten (W),tantalum (Ta), molybdenum (Mo), platinum (Pt), palladium (Pd), gold(Au), among others, as well as alloys comprising at least one of theforegoing metals, and mixtures comprising at least one of the foregoingmetals. Some possible alloys include a nickel-phosphorus (NiP) alloy, apalladium-phosphorus (PdP) alloy, a cobalt-phosphorus (CoP) alloy, anickel-cobalt (NiCo) alloy, a gold-cobalt alloy (AuCo), and acobalt-tungsten-phosphorus (CoWP) alloy.

Electroforming process parameters include solution temperature,composition, and rectifier voltage. Regarding the temperature, thesolution in the electroforming tank can optionally be heated to about30° C. to about 80° C., or, more specifically, about 35° C. to about 60°C., or, even more specifically, about 40° C. to about 50° C. Therectifier can be used to apply a sufficient voltage to the electrodes toinduce an electric current to cause anodic oxidation of the metal to bedeposited, and to reduce the metal ions at the cathode. For theformation of a Ni or Ni alloy layer, for example, the current densitycan be about 2 amperes per square foot (ASF) to about 100 ASF or so, or,more specifically, about 5 ASF to about 60 ASF or, even morespecifically, about 10 ASF to about 30 ASF.

The exposure time in the electroforming tank while the current isapplied can be determined based upon the particular metal layer to beformed and the desired thickness of that layer. The layer thickness canbe based upon a desired structural integrity to enable the layer to beremoved from the master as well as to be used to produce next generationsub-masters, and based upon the size of the features formed in thesurface of the layer. Thicknesses can be up to and exceeding about 500micrometers (μm) or so, or, more specifically, about 50 μm to about 400μm, or, even more specifically, about 100 μm to about 300 μm, and, yetmore specifically, about 150 μm to about 250 μm.

By controlling the processing parameters of the electroplating, thethickness of the deposited metal layer can be adjusted. The thickness ofthis metal layer can be calculated from the equation:$T = \left( \frac{M \cdot I \cdot t}{{Z}F\quad\rho\quad A} \right)$

-   -   where: T=thickness of the electroformed layer;        -   M=the molar mass of the metal;        -   I=the current;        -   t=the time of electroformation;        -   |Z|=the absolute value of the valence of the metal;        -   F=Faraday constant;        -   ρ=the density of the metal; and        -   A=the surface area to be covered by the metal.            This equation gives a theoretical maximum thickness assuming            100% efficiency of the cathode. However, because electrodes            are not always 100% efficient, the actual thickness is            usually less than that calculated by the equation.            Generally, the efficiency of an electrode is about 95% to            about 99% depending on the material used as well as other            factors.

Once the desired thickness is achieved, rectifier is switched off andthe cylinder is removed from the electroforming tank. Optionally, thecoated master is rinsed, e.g., with water (such as deionized water(i.e., water that has been treated with an ion exchange resin to removeions therefrom)), and retained in an inert environment (e.g., anenvironment that does not chemically interact with the sub-mastersurface to change the surface chemistry under the environmentalconditions). Some possible inert environments include nitrogen, argon,helium, vacuum, and others, depending upon the environment.

The sub-master, comprising a negative of the structures on the master,can be separated from the master. For example, if a separation tape(also know as plater's tape) has been disposed on the master, the tapecan be removed from the master, exposing the master as well as an edgeof the sub-master. The sub-master can then be peeled from the master.The master can again be used to produce additional generations ofsub-masters by repeating the masking, passivation, plating, andseparation.

The sub-master thus produced, can then be used to make next generationsub-masters (e.g., shims). Prior to employing the sub-master in theplating process, the sub-master can optionally be annealed. Theannealing can be employed to flatten the sub-master into a sheet-likeform, for example, for ease in production of a subsequent generation ofsub-masters. The sub-master, once removed from the master, has a roundedshape, e.g., a partial cylinder. Therefore, the sub-master can be heatedto a sufficient temperature to change the shape of the sub-master from acylinder-like to a sheet or plate-like sub-master. The particularannealing temperature is based upon the sub-master composition as wellas the annealing time. The particular temperature employed issufficiently high to soften the sub-master such that it forms a sheet ina chosen time, while sufficiently low to avoid undesirable surfacereactions as well as adversely affecting the sub-master's surfacefeatures. The upper temperature limit is based upon the meltingtemperature of the sub-master material, as well as the possiblereactions and adverse effects that the heat may have on the surfacefeatures, while the lower temperature limit is based upon a practicalamount of time to convert the overall shape of the sub-master to asheet-like form. At the higher temperatures, an inert environment can beemployed.

With Ni and Ni alloy sub-masters, for example, annealing can beaccomplished at a temperature of about 200° C. to about 400° C., or,more specifically, about 200° C. to about 300° C., or, even morespecifically, about 225° C. to about 275° C. These temperatures can beemployed for periods of time of about 3 hours to about 10 hours, or,more specifically, about 4 hours to about 7 hours.

Optionally, the annealed sub-master can be mounted to a stiffener plateto enhance the structural integrity of the sub-master. The stiffenerplate can comprise any material that will provide the desired structuralintegrity to the sub-master, will not react with the plating solutionand/or the sub-master under the plating conditions. Possible stiffenerplates include materials such as aluminum, ferrous materials (e.g.,stainless steel), and so forth, as well as combinations comprising atleast one of the foregoing materials.

The sub-master can be mounted to the stiffener plate with variousadhesives, such as a non-conductive vinyl adhesive, double-faced tape(e.g., pressure sensitive, double-faced tape). The tape adhesive cancomprise rubber, acrylic, silicone, and combinations comprising at leastone of the foregoing adhesives. The adhesives can be applied to theplate and contacted with a rubber roll to attain good adhesion.Optionally, the plate can then be placed in a vacuum bag where a vacuumcan be applied to evacuate air from the space between the sub-master andthe plate, eliminating air voids. In other words, the pressure in thebag can be reduced to below the pressure of the atmosphere surroundingthe bag.

In another embodiment, the sub-master can be attached to the stiffenerplate using magnetic force. For example, the plate could have permanentand/or electromagnets imbedded therein, and/or magnetic sheeting (e.g.,vinyl magnetic sheeting) can be adhered to the surface of the stiffenerplate.

The mounted sub-master can then be masked to prevent the subsequentdeposition of the metal layer onto the stiffener plate, as well as ontoundesirable areas of the sub-master. Various masking materialscompatible with the plating environment as well as the stiffener plateand sub-master, can be employed. Some exemplary materials include vinyltape, polyimide tape, and polyester tape, among others. The polyestertape has been found to be chemically resistant and consequently reusablefor several plating cycles. The adhesive on the tape can comprisevarious adhesives compatible with the plating environment, such assilicone. The mask can be applied to the back of the plate and theperimeter of the front of the plate to define the plating area for theelectroforming step.

Connection areas can then be cut through the tape, e.g., at the shortedges of the sub-master, to expose the mounting plate. Conductivematerial can then be employed to connect the stiffener plate and thesub-master. The conductive material can be a metal such as nickel,aluminum, stainless steel, copper, and combinations comprising at leastone of the foregoing metals. For example, metal foil tape can be appliedto the connection area and conductive sealer (e.g., conductive paint)can be disposed around the copper tape to ensure conductivity betweenthe sub-master and the stiffener plate (wherein the foil tape has aconductive adhesive).

In order to form sub-masters with a taping area, e.g., to inhibitsurface area yield loss in the subsequent generations of sub-masters,the sub-master can optionally be mounted on an oversized stiffenerplate. This stiffener plate can have a larger surface area than thesub-master such that, on the side of the stiffener plate where thesub-master is mounted with adhesive (e.g., double-faced tape), there isan area of stiffener plate surface that extends beyond the perimeter ofthe sub-master; e.g., that forms a boarder around the sub-master. Thesize of the desired border is application dependent. A border can beformed having a width of up to about 5 inches (12.7 centimeters (cm) orso, or, more specifically, about 0.25 inches (0.6 cm) to about 4 inches(10.2 cm), or, even more specifically, about 0.5 inches (1.3 cm) toabout 3 inches (7.6 cm), and, yet more specifically, about 1 inch (2.5cm) to about 2 inches (5.1 cm).

A conductive rim can then be disposed on the exposed surface of thestiffener plate, overlaying the edges of the sub-master. The conductiverim can be formed with any conductive material that is compatible withthe plating environment and materials, and that can be adhered to thestiffener plate. Possible conductive materials include stainless steel,copper, nickel, and silver, among other conductive materials. Possibleforms for the conductive material include sheets, tapes (such aspressure sensitive tape), paintable liquids and/or pastes containingmetals, among others.

If the adhesive on the tape used to form the conductive rim is notelectrically conductive, a conductive material such as a conductivepaint can be applied to the seam between the sub-master and theconductive rim. The conductive material can be dried (actively orpassively), sanded smooth to remove over-painted regions, therebyforming an extended sub-master. The mounted sub-master can then bemasked as described above, leaving at least a portion of the conductiverim exposed. Here, due to the presence of the conductive rim, when theelectroform is deposited (e.g., via chemical vapor deposition, plasmaspraying, in an electroforming bath, or otherwise), the next generationsub-master produced will have a non-surface feature area that forms aperiphery or frame around the surface feature area. This periphery canthen be used for the masking and adhesion in the production ofsubsequent generations of sub-masters whereby the loss of surface areain the surface feature region is minimized because the non-surfacefeature frame can be sacrificed if trimming of the periphery is needed.

The mounted sub-master can be connected to electrode(s) through the backof the stiffener plate. For example, copper electrode(s) can be securedto the back of the stiffener plate with copper screws.

The masked sub-master can then optionally be disposed in a box (e.g., aframe such that the mounted sub-master forms the back of the box), wherethe edges of the frame are sealed to the plate with sealant. Forexample, the mounted sub-master is placed in a box (such as apre-machined box formed from an electrically non-conductive materialsuch as glass, plastic (e.g., polyvinyl fluoride), and/or the like) andsealed to the masked sub-master with sealant such as a silicone sealant.The frame may help facilitate the even distribution of the metal layeron the sub-master, inhibiting buildup at the edges thereof.

The sub-master can be used in the plating process to create additionalelectroforms so long as the surface to be plated is properly passivated.As noted above, passivation helps to prevent the next generationsub-master from adhering to the surface of the prior generationsub-master once formed. Controlling various parameters of thepassivation layer affect the life of the sub-master (e.g., the number ofcopies that can be made from the sub-master while retaining macroscale,microscale, and nanoscale resolution). Macroscale refers to thereproduction in the next generation sub-master of the overall geometryof the replica, such as flatness and visual uniformity. Thismacrostructure has a size of approximately 1 millimeter (mm) to about 1meter (m) or the entire size of the part being formed; i.e. of a sizescale easily discerned by the human eye. Microscale refers to thereproduction in the next generation sub-master of microstructures on thesurface, such as hemispheres, corner-cubes, microlenses, prisms, and soforth, as well as combinations comprising at least one of the foregoing.These microstructures have a size of less than or equal to about 1 mm,or, more specifically, greater than 100 nanometers (nm) to about 1 mm.Nanoscale resolution refers to the reproduction in the next generationsub-master of nanostructures forming part of a surface feature, such asat or near corners or a peak or valley of a surface feature, or theoptical smoothness of a facet of a feature. These nanostructures have asize of less than or equal to about 500 nm, or, more specifically, lessthan or equal to about 100 nm, or, even more specifically, less than orequal to about 20 nm, and yet more specifically, about 0.5 nm to 10 nm.

The parameters that can be controlled that can affect the life of thesub-master include the chemical composition, the thickness, density, anddistribution of the passivation layer. By controlling the passivationlayer, greater than or equal to about 50, or, more specifically, greaterthan or equal to about 75, or, even more specifically, greater than orequal to about 100, and even expect hundreds of sub-masters from nickelalloy electroform replicas having the nanoscale resolution can beproduced.

The particular passivation employed for the sub-master is dependent uponthe sub-master material. Passivation can be accomplished, for example,by contacting the sub-master with a solution (e.g., an aqueous solution)and anodically charging the sub-master. The aqueous solution cancomprise a surfactant and be alkaline (e.g., have an alkalinity ofgreater than or equal to pH 8, or, more specifically, greater than orequal to about 10, or, even more specifically, a pH of about 12 to about14).

The surfactant can be any material that reduces the surface tension ofwater and aids the wetting of the metal surface. Possible surfactantsinclude cationic, non-ionic, anionic, as well as combinations comprisingat least one of the foregoing surfactants. Anionic surfactants include,for example, carboxylates, sulfonates, sulfates, and phosphate esters.Cationic surfactants include, for example, amines and quaternary salts.Non-ionic surfactants include, for example, polyoxyethylene derivativesof fatty alcohols, carboxylic esters, and carboxylic amides.

The alkalinity can be attained with a material capable of promoting orcausing the formation of metal oxides and/or metal hydroxides on thesurface of the sub-master, e.g., an oxidation species. Some possibleoxidation species that can be employed include alkali metal hydroxides(such as sodium hydroxide, potassium hydroxide, and the like), as wellas combinations comprising at least one of the foregoing.

Once the sub-master is disposed in the aqueous solution, it isanodically charged to convert metallic components on the surface thereofto metal oxides and/or metal hydroxides, thereby forming a passivationlayer. The sub-master can be charged until the passivation layer has athickness of about 10 Angstroms (Å) to about 500 Å, or, morespecifically, about 15 Å to about 60 Å, or, even more specifically,about 20 Å to about 40 Å. The amount of current applied to thesub-master can be about 1 ASF to about 40 ASF, or, more specifically,about 5 ASF to about 25 ASF, or, even more specifically, about 5 ASF toabout 10 ASF. This current can be applied for a period of about 1 minuteto about 5 minutes, or, more specifically, about 1 minute to about 3minutes.

This passivation technique has been found particularly useful with Nicontaining sub-masters (e.g., comprising Ni and/or a Ni alloy (e.g.,NiCo, NiCr, among others)). For the Ni containing sub-masters, a greaternumber of successful replication of the nanostructures was achieved whenemploying a solution comprising an alkali metal hydroxide instead of achromate. Possible alkali metal hydroxides include sodium hydroxide,potassium hydroxide, and the like, as well as combinations comprising atleast one of the foregoing.

Once passivated, the sub-master can optionally be dried (passivelyand/or actively), and then plated. Plating can be in various fashionsthat are capable of applying a layer of metal onto the surface of theelectroform and thereby replicating the surface features thereof. Forexample, the passivated electroform can be placed in a solution in theelectroforming tank. Electrical connection is made to the surface of thesub-master comprising the surface features so that it becomes thecathode. This solution in the electroforming tank can comprise about 60g/l to about 100 g/l of metal sulfamate (e.g., the metal to bedeposited), sufficient acid to attain a pH of less than or equal toabout 6, a sufficient amount of surfactant agent to affect wetting ofthe metallic surface to be coated, and optionally a hardening agent,e.g., to control stress in the deposit. For example, the solution cancomprise about 70 g/l to about 90 g/l metal alloy sulfamate (e.g.,nickel-cobalt sulfamate, cobalt-tungsten sulfamate, and so forth), about25 g/l to about 35 g/l boric acid, and sufficient sulfamic acid toattain a pH of about 2 to about 5.0. The anode, as stated above,optionally comprises the metal or metals to be deposited on thesub-master surface.

When a current is applied to the system, the anodic metal oxidizes toform metal ions which then flow to the cathode (the surface of thepassivated sub-master) and deposit thereon. The cathode then reduces themetal ion into elemental metal. Once the desired thickness of thedeposited metal has been achieved, the current is ceased and the platedsub-master is removed from the tank.

The thickness of the layer formed on the sub-master, which is a positiveof the sub-master, is dependent on its use, for example, to producefurther generations of sub-masters or to produce final product. Thethickness can be greater than the depth of the features on thesub-master and sufficient to attain the structural integrity for itsintended use. The layer thickness can be based upon a desired structuralintegrity to enable the layer to be removed from the master as well asto be used to produce next generation sub-masters. Thicknesses can be upto and exceeding about 500 micrometers (μm) or so, or, morespecifically, about 50 μm to about 400 μm, or, even more specifically,about 100 μm to about 300 μm, and, yet more specifically, about 150 μmto about 250 μm.

In some applications it may be desirable to form a multi-layerelectroform, e.g., for the final generation tooling (i.e., theelectroform employed to make final product such as prismatic films). Forexample, a single electroform that is produced with layers of differentcompositions. Each layer can have the same or a different thickness. Forexample, the surface layer (i.e., the layer the side of the electroformcomprising the surface features), can be a material that enhances therelease of the final product from the electroform, and/or that inhibitsundesired reactions on the surface, while the back layer can be amaterial that enhances the structural integrity of the electroform. Oneor more intermediate layers can also be employed, e.g., to enhance thebonding of the other layers.

For example, a surface layer comprising gold (e.g., gold, a gold alloy,or a gold mixture) can be plated onto a sub-master, and then backinglayer comprising nickel (e.g., nickel, a nickel alloy, or a nickelmixture) can be overplated (plated over the gold). In this process, thesub-master is passivated as described above. The passivated sub-mastercan then be disposed into an electroplating bath comprising the desiredsurface-layer material (e.g., gold). The surface layer can then beformed utilizing the sub-master as the cathode in the electroplatingprocess. Once the desired surface layer thickness has been achieved, thesub-master can then be disposed in a second electroplating solution toform the second layer onto the surface layer. Again, the sub-master canbe used as the cathode in the electroplating process. The thickness ofthe second layer is dependent upon a desired overall electroformthickness and the function of this second layer, e.g., as anintermediate layer or as the backing layer. Although passivation of thesub-master between the electroplating solutions is possible, the variouslayers can be formed without this passivation so that each layer of themultilayer electroform is firmly bonded to the next.

The thickness of the surface layer is dependent upon the particularapplication. The surface layer can have a thickness of millimeters insome applications, while it can be nanometers thick in others. Forexample, where the surface layer is employed to attain a chemicalinertness on the surface of the electroform while controlling the costsof the layer (e.g., while limiting the amount of gold in the layer), thesurface layer can have a thickness of up to about 10 μm or so, or, morespecifically, about 1 nm to about 1 μm, or, even more specifically,about 5 nm to about 500 nm, and yet more specifically, about 10 nm toabout 100 nm. An intermediate layer can have a thickness of up to about50 micrometers (μm) or so, or, more specifically, about 1 nm to about 25μm, or, even more specifically, about 10 nm to about 1 μm. The backinglayer can have a thickness of up to about 500 micrometers (μm) or so,or, more specifically, about 50 μm to about 400 μm, or, even morespecifically, about 100 μm to about 300 μm.

For example, a passivated sub-master can be passivated in an alkalinesolution by anodically charging the sub-master. Once a passivation layerhas been formed, the passivated electroform can be removed from thealkaline solution and optionally rinsed. The passivated electroform canthen be disposed in the surface layer electroplating solution comprisinggold cyamide, silver cyamide, and so forth. A current is applied, and,with the passivated electroform acting as the cathode, metal ions (e.g.,gold, silver, cobalt, nickel, and so forth, depending on the compositionof the solution) are deposited on the surface of the sub-master.

Once a desired surface layer thickness has been attained, the coatedelectroform is moved to the next electroplating solution comprising themetals to be disposed in the subsequent layer (e.g., comprising nickel,cobalt, and so forth). Optionally, the coated electroform can be rinsed(e.g., with deionized water) prior to entering the subsequentelectroplating solution. Furthermore, maintenance of the coatedelectroform in an inert environment can be desirable (i.e., anenvironment that will not cause a reaction on the surface layer). In thesubsequent electroplating solution, the coated sub-master againfunctions as the cathode and receives metal ions on its surface. Thisprocess can be repeated until the desired number of layers and layerthicknesses has been attained.

It has been discovered that the formation of an inert coating layer onthe surface of the final generation sub-master enhances the life of thesub-master. For example, a surface layer comprising gold (e.g., agold-cobalt surface layer with a nickel-cobalt backing layer) isparticularly useful with acrylate coating material. Not to be bound bytheory, where the acrylate coating material would react with the surfaceof a nickel-cobalt electroform, causing building-up nodules of solidcrosslinked coating on the surface of the tool. These nodules grow insize and number over successive copies of the tool on the coater. Theyare also replicated on the films produced with that electroform. Evenwhen the nodules are less than 100 nm in size (as measured along a majoraccess), they can adversely effect the replication of nanostructuresfrom the electroform. When the grow to about 200 nm to about 400 nm insize, they are large enough to scatter light (preferentially scatteringblue light) and give the film product a blue hazy appearance. At thispoint, for a product requiring nanostructure replication, the product isrejected and the tool is scrapped. Depending on the coating formulation,the failure point can be as little as 100 copies or as many as a fewthousand copies, where manufacturing efficiency requires tens ofthousands of copies, and even hundreds of thousands of copies from asingle electroform to be efficient and production viable. By employingthe inert surface layer on the electroform, using the same productcoating formulation that caused failure of a single layer electroformafter 100 copies, 30,000 copies were produced with no nodule formation(as confirmed with a high resolution scanning electron microscope(SEM)).

A further advantage of the multilayer electroform is its surfaceproperties are changes which gives enhanced release of the coating(e.g., plastic replication material) from the electroform in the plasticreplication process. For example, a cured acrylate coating peeled off ofthe multilayer electroform with less force than from a single layerelectroform. If the coating sticks to the electroform it can tear,leading to a point defect forming on the tool where a bit of the plasticmaterial stuck to the sub-master. This debris replicates into everysubsequently-produced plastic film, causing rejection of all productsthus formed and production must be stopped and the tool discarded. Whenforming single layer electroforms, defects could be developed within themaking of 300 to 2,000 plastic films, while, with the use of multilayerelectroforms (e.g., with a surface layer comprising gold), at leastabout 20,000 to about 30,000 plastic films could be made without theformation of point defects.

Since the plated sub-master is flat, separation of the 2^(nd) generationsub-master can be accomplished by peeling the electroform (i.e., theplating) from the sub-master. As noted above it is desirable touniformly remove the sub-master from the substrate without twisting ortorquing the sub-master. Twisting, torquing, and other non-uniformremoval can damage the pattern on the surface of the next generationsub-master and potentially even damage the surface of the sub-masterbeing replicated.

The 1^(st) generation sub-master can be employed to make additional2^(nd) generation sub-masters by repeating the passivation, plating, andseparation. Depending upon the materials used for the mounting andmasking, one or several 2^(nd) generation sub-master may be producedprior to replacing those materials.

The 2^(nd) generation sub-master can be employed to make 3^(rd)generation sub-masters or to make final product, e.g., film withmicrostructures having nanoscale resolutions, and in particular, filmscomprising light-reflecting elements (e.g., retroreflective elements).Possible microstructures include light-reflecting elements such ascube-corners (e.g., triangular pyramid), trihedral, hemispheres, prisms,ellipses, tetragonal, grooves, channels, microlenses, and others, aswell as combinations comprising at least one of the foregoing.

The particular post-treatment(s) employed prior to using a sub-master inthe production of product are dependent upon the particular product tobe formed. For example, to produce an acrylate film comprising thedesired nanoscale resolution, the surface energy of the sub-master canbe reduced (e.g., of a nickel containing sub-master). Desirably, thepost-treatment renders the surface of the electroform hydrophobic, andas such, will not attract polar molecules such as organic monomers andin particular acrylate monomers.

High surface energy surfaces can attract polar molecules and becomewetted with them. In the case of water being the polar species, thesurface is wetted with water, there being a low wetting angle, and thesurface is said to be “hydrophilic.” Low surface energy surfaces willnot attract polar molecules and will not become wetted with them. If thesurface is rendered to be of a low surface energy then polar specieslike water will bead-up on the surface, and the surface is said to be“hydrophobic.”

The surface energy of the sub-master surface can be reduced by treatingthe sub-master with a solution having a pH of less than or equal to 6,or, more specifically, less than or equal to about 5, or, even morespecifically, about 2 to about 5. Optionally, a cathodic current can beapplied. The cathodic current can have a current density of about 1 ASFto about 60 ASF, or, more specifically, about 2 ASF to about 30 ASF or,even more specifically, about 2 ASF to about 10 ASF.

The sub-master can also, optionally, be treated to remove particulate(s)and/or staining (e.g., after the sub-master has been used to makeproduct). This treatment can be before the sub-master has been used toproduce product, and/or to refurbish the sub-master. This post-treatmentcan comprise rinsing the sub-master with water (e.g., deionized water),acidic media, and/or caustic media. For example, the sub-master can beplaced in a bath containing deionized water, aqueous acid (e.g., a pH ofless than or equal to about 6, or, more specifically, a pH of about 2 toabout 5), and/or caustic media (e.g., a pH of greater than or equal toabout 8, or, more specifically, a pH of about 8 to about 14).

Once removed from the bath, the sub-master can be rinsed with water(e.g., deionized water), for example, to remove particulates and metalsalts. The sub-master can then be actively (e.g., contacted the heat,gas, and/or another method of facilitating drying) and/or passivelydried. Optionally, the sub-master can be oven dried at a temperaturethat does not adversely affect the surface features or surfacechemistry.

When used to make a product (e.g., to mass produce product such as LCDdisplays to diffuse or collimate light), the electroform (e.g., anelectroform that has been post-treated with a cathodic current), can beattached to a calendaring roll. Product material can then be applied tothe electroform. For example, a desired film material(s) can be extruded(or co-extruded) such that the material that will comprise the surfacefeature is disposed in direct physical contact with the electroform. Thematerial can be cured and removed from the electroform to form theproduct. As an alternative, and/or in addition to the extrusion,preformed film(s) can be employed. Here, the film to be imprinted withthe surface features can be sufficiently heated to enable the formationof the surface features into the film surface.

Possible product materials include plastics (e.g., thermoplastics and/orthermosets), such as acrylates, polycarbonates, polyesters,terephthalates (e.g., poly(ethylene terephthalate)), polyimides (e.g.,polyetherimides), polystyrenes (e.g., ABS, ASA, and so forth),polyolefins, polyacrylonitrile (PAN), polyamide (PA), polyvinyl chloride(PVC), resorcinol, polyarylenes (e.g., polyarylene ether),polyacrylonitrile, polyethers, as well as combinations comprising atleast one of the foregoing plastics. Various plastics can be combined ina single layer. These plastics can also be disposed in separate layersto form the product wherein one of the layers comprises the desiredsurface features. If multilayers are employed, adjacent layers comprisematerials that provide sufficient adhesion between the layers for thedesired application (e.g., that will not delaminate under use conditionsfor the product). Optionally, coatings and the like can be applied tothe product after the surface features have been disposed in the surfacethereof. Possible films that can be produced with the present processinclude those disclosed in U.S. Published Application No. 2003/0214728A1 to Olczak, U.S. Published Application No. 2004/0109663 A1 to Olczak,and others.

In FIG. 2 a cross sectional view of a backlight display device 100 isshown. The backlight display device 100 comprises an optical source 102for generating light 104. A light guide 106 guides the light 104therealong by total internal reflection (TIR). The light guide 106contains disruptive features that cause the light 104 to escape thelight guide 106. A reflective substrate 108 positioned along the lowersurface of the light guide 106 reflects any light 104 escaping from thelower surface of the light guide 106 back through the light guide 106and toward an optical substrate 110. At least one optical substrate 110is receptive of the light 104 from the light guide 106. The opticalsubstrates 110 comprise a three-dimensional surface 112 defined byprismatic structures 116 (FIGS. 3, 4, 5, and 6).

The optical substrates 110 may be positioned, one above the other, in acrossed configuration wherein the prismatic structures 116 arepositioned at an angle with respect to one another (e.g., 90 degrees).The prisms 116 have a prescribed peak angle, α, a height, h, a length,l, and a pitch, p and one or both of the prismatic surfaces 112 may berandomized in their peak angle, α, height, h, length, l, and pitch, p.Yet further, one or both sides of the substrates 110 may have the prisms116. In FIGS. 3, 4, and 5 the sidewall or facets 132 of the prisms 116,which comprise the surface 112, are curved. The curvature can bedescribed as a segment of a parabola, or more generally as a polynomialsurface given by the sag equation: $\begin{matrix}{z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {dr}^{2} + {er}^{4} + {fr}^{6} + {{Higher}\quad{order}\quad{terms}\quad{in}\quad r}}} & (2)\end{matrix}$where z is the perpendicular deviation (or “sag”) in microns of thesidewall or facet 132 of the prisms 116 from a straight reference line128, originating at a first reference point (b) at a base of the prismand terminating at a second reference point (a) near the peak of theprism and c-1 is the radius of curvature of the facet. Here thecoefficients of the polynomial may have the following approximateranges: −20<c<20, −10<d<10, −10<e<10, −10<f<10, and −1<k or less than orequal to zero wherein r is a radial coordinate or distance from anoptical axis in microns. It is noted that c²r² is greater than or equalto zero and less than or equal to 1. Odd order terms in r (e.g., r¹, r³,r⁵, r⁷, etc.) with appropriately chosen coefficients may also be used asin Eq. 2. The higher order terms for the even and odd order terms haveappropriately chosen coefficients. Terms other than the first r² termmay be written as: $\sum\limits_{i = 1}^{N}{a_{i}{r^{i}.}}$

Linear segments or other approximations to the polynomial described byEq. 2 may also be used. Linear segments result in a compound angle prismhaving a first facet 126 at an angle of θ and a second facet 124 at anangle of β. As best understood from FIG. 6, the curvature of the curvedsidewall or facet 132 of the prisms 116 can be either convex or concave.In FIG. 6, the side facets of the prism are positioned so as to form oneor more compound facets 124, 126, respectively subtending an angle of βor θ with the base of the prism.

The light-redirecting structure can be created, for example, by applyingthe curable coating to the base film and casting the desiredlight-redirecting structure in the curable coating, by hot-embossing thestructure directly onto the base film, or the like. While the base filmmaterial can vary depending on the application, suitable materialsinclude those base film materials discussed in published U.S. PatentApplication No. 2003/0108710 to Coyle et al. More specifically, the basefilm material of the brightness enhancement film can comprise metal,paper, acrylics, polycarbonates, phenolics, cellulose acetate butyrate,cellulose acetate propionate, poly(ether sulfone), poly(methylmethacrylate), polyurethane, polyester, poly(vinylchloride),polyethylene terephthalate, and the like, as well as blends copolymers,reaction productions, and combinations comprising at least one of theforegoing.

The following examples are provided merely to further illustrate theelectroforms and the methods described herein, and are not intended tolimit the scope hereof.

EXAMPLES Example 1 Passivation in a Caustic Solution with Anodic Current

Sample 1, a nickel sub-master electroform having a microstructurecomprising a plurality of channels and grooves of about 1 μm to about 37μm in depth, was passivated by immersion into an aqueous solution for 4minutes at 25° C. while applying an anodic current density of 4 ASF. Theaqueous solution comprised 20 g/l potassium hydroxide and 0.5 g/l sodiumlauryl sulfate and had a pH of 13.5. The sub-master was removed, rinsedwith deionized water, and then dried. The sub-master master was thenplated with a nickel-cobalt (NiCo) alloy by electroforming a layer thatwas about 100 μm in thickness. After electroforming, the platedsub-master was rinsed and dried, and the nickel-cobalt electroform wasreadily peeled from the sub-master, showing complete removal and novisible damage to the microstructures when examined under a microscopeat up to 40×. It is also noted that samples have been examined to amagnification of 100× without visible damages, and even passed SEM(scanning electron microscope) review at 100KX (100,000×).

Example 2 Passivation in a Caustic Solution with Anodic Current

Sample 2, a nickel sub-master electroform having a microstructurecomprising a plurality of channels and grooves of about 1 μm to about 37μm in depth, was passivated by immersion into an aqueous solution for 4minutes at 35° C. while applying an anodic current density of 4 ASF. Theaqueous solution comprised 20 g/l of StamperPrep (a high alkalinity (pHgreater than 13), low foaming, cleaning agent comprising sodiumhydroxide commercially available from DisChem, Inc., Ridgway, Pa.), andhad a pH of greater than 13.5. The sub-master was removed, rinsed withdeionized water, and then dried. The sub-master was then plated with anickel-cobalt alloy by electroforming a layer that was about 100 μm inthickness under the same conditions as in Example 1. Afterelectroforming, the plated sub-master was rinsed and dried, and thenickel-cobalt electroform was readily peeled from the sub-master,showing complete removal and no visible damage to the microstructureswhen examined under a microscope.

Example 3 Passivation of a Nickel Containing Sub-Master

Sample 3, a nickel sub-master electroform having a microstructurecomprising a plurality of channels and grooves of about 1 μm to about 37μm in depth, was passivated by immersion into an aqueous solution for 30seconds at 35° C. while applying an anodic current density of 35 ASF.The aqueous solution comprised 90 g/l of StamperPrep, and had a pH ofgreater than 13.5. The sub-master was removed, rinsed with deionizedwater, and then dried. The sub-master was then plated with anickel-cobalt alloy by electroforming a layer that was about 100 μm inthickness under the same conditions as in Example 1. Afterelectroforming, the plated sub-master was rinsed and dried, and thenickel-cobalt electroform was readily peeled from the sub-master,showing complete removal and no visible damage to the microstructureswhen examined under a microscope.

Example 4 Passivation of a Nickel Containing Sub-Master

Sample 4, a production-size nickel-cobalt sub-master electroform (anominal size of 40 centimeters (cm) by 65 cm), having a microstructurecomprising a plurality of channels and grooves of about 1 μm to about 37μm in depth, was passivated by immersion into an aqueous solution for 4minutes at 35° C. while applying an anodic current density of 4 ASF. Theaqueous solution comprised 20 g/l of StamperPrep, and had a pH ofgreater than 13.5. The sub-master was removed, rinsed with deionizedwater, and then dried. The sub-master was then plated with anickel-cobalt alloy by electroforming a layer that was about 200 μm inthickness under the same conditions as in Example 1. Afterelectroforming, the plated sub-master was rinsed and dried, and thenickel-cobalt electroform was readily peeled from the sub-master,showing complete removal and no visible damage to the microstructureswhen examined under a microscope.

Sample 4 was then recycled through the passivation step andelectroforming step a total of 57 times, thus generating 57 electroformsall of which separated cleanly and wholly, showing complete removal andno visible damage to the microstructures when examined under amicroscope.

Example 5 Passivation of a Nickel Containing Sub-Master

Sample 5, a production-size nickel-cobalt sub-master electroform (anominal size 40 cm by 65 cm), having a microstructure comprising aplurality of channels and grooves of about 1 μm to about 37 μm in depth,was passivated by immersion into an aqueous solution for 4 minutes at35° C. while applying an anodic current density of 4 ASF. The aqueoussolution comprised 20 g/l of StamperPrep, and had a pH of greater than13.5. The sub-master was removed, rinsed with deionized water, and thendried. The sub-master was then plated with a nickel-cobalt alloy byelectroforming a layer that was about 200 μm in thickness under the sameconditions as in Example 1. After electroforming, the plated sub-masterwas rinsed and dried, and the nickel-cobalt electroform was readilypeeled from the sub-master, showing complete removal and no visibledamage to the microstructures when examined under a microscope.

Sample 5 was then recycled through the passivation step andelectroforming step a total of 65 times, thus generating 65 electroformsall of which separated cleaning and wholly showing complete removing andwith no visible damage to the microstructures when examined under amicroscope.

Example 6 Passivation of a Nickel Containing Sub-Master with a SolutionComprising Dichromate

A nickel-cobalt sub-master electroform having a microstructurecomprising a plurality of channels and grooves of about 1 μm to about 37μm in depth was passivated by immersion into an aqueous solutioncomprising 5 g/l potassium dichromate for 5 minute at 25° C. whileagitating the solution. The sub-master was removed and rinsed withdeionized water. The sub-master was then plated with a nickel-cobaltalloy by electroforming a layer that was about 100 μm in thickness.After electroforming, the plated sub-master was rinsed and dried, andthe nickel-cobalt electroform was peeled from the sub-master.Examination under a microscope showed the microstructures to bepartially damaged, whereas the very finest structures at the sharpestcorners of the peaks were torn from the electroform and remained on thesub-master, thus causing visible defects and loss of opticalperformance. The dichromate passivation process was inadequate topassivate the nickel containing sub-master in that not all areas (inparticular, the deepest valleys on the sub-master), were passivatedsufficiently to allow complete removal of the entire electroform copy.

Example 7 Post-Treatment by Immersion in a Caustic Solution, Followed byRinsing and Drying

An electroform, such as Sample 1, can be immersed in a caustic solutionhaving a pH of about 8 to 14, at 40° C., for 1 to 5 minutes, rinsed withdeionized water, and dried. The electroform can then be placed on a rollfor use in the formation of acrylate films. A liquid coating mixture,comprising UV-curable acrylate monomer(s), oligomer, photoinitiator, andnon-reactive additive(s), can be pressed into the electroform surface bya backing film, (e.g., a plastic film, such as polycarbonate, polyester,and so forth, as well as reaction products comprising at least one ofthe foregoing, and combinations comprising at least one of theforegoing), and can be cured to fix the microstructures into thesurface. The film, with the cured acrylate microstructures, can then beseparated from the roll. It has been observed that electroforms, such asSample 1, (that have only been rinsed, but not post-treated to reducethe surface energy), i.e., with a high surface energy, cause permanentsticking of minute domains of the acrylate coating during the productionof the transparent film. These minute domains accumulate on theelectroform surface, ultimately changing the surface features, andthereby effectively causing the loss of the desired nanoscaleresolution.

Example 8 Post-Treatment by Immersion in an Acidic Solution andApplication of a Reverse Current (Cathodic Current)

Sample 7, a NiCo sub-master such as Sample 1, can be post-treated, e.g.,to reduce the surface energy. Sample 7 can be immersed in an acidicsolution for 1 to 5 min at 40° C., while applying a cathodic currentdensity of 4 ASF. The acidic solution can comprise Citranox™, and canhave a pH of about 4. The electroform can then be placed on a roll foruse in the formation of acrylate films. A liquid coating mixture,comprising UV-curable acrylate monomer(s), oligomer, photoinitiator, andnon-reactive additive(s), can be pressed into the electroform surface bya backing film, (such as polycarbonate, polyester, and so forth), andcan be cured to fix the microstructures into the surface. The film, withthe cured acrylate microstructures, can then be separated from the roll.This acrylate film has been observed to have a nanoscale resolution.

Example 9 Treatment by Immersion in a Caustic Solution (After Productionof Product with the Electroform)

Sample 8, a NiCo sub-master such as Sample 1, can be post-treated, e.g.,to reduce the surface energy. Sample 8 can be immersed in a causticmedia for 1 to 5 min at 40° C., while applying a cathodic currentdensity of 4 ASF. The caustic solution can comprise StamperPrep™, sodiumhydroxide, etc., and can have a pH of about 8 to about 14. Theelectroform can then be placed on a roll for use in the formation ofacrylate films. A liquid coating mixture, comprising UV-curable acrylatemonomer(s), oligomer, photoinitiator, and non-reactive additive(s), canbe pressed into the electroform surface by a backing film, (such aspolycarbonate, polyester, and so forth), and can be cured to fix themicrostructures into the surface. The film, with the cured acrylatemicrostructures, can then be separated from the roll. It was furtherobserved that the caustic soak and reverse current, when applied to thenickel or nickel-cobalt electroforms, also eliminated particulate andstaining defects from the microstructured electroform surface, whichresulted in tool yield improvements.

The electroforms prepared as described herein can be use to produceacrylate films, e.g., display films with microscale features. For suchbrightness enhancement films, the key optical property to be measured isthe on-axis luminance of these films in an LCD backlight assembly, whichwas measured with using the following protocol. A Teijin D120(commercially available from Tsujiden Co., Ltd., Japan) bottom diffuserwas placed on backlight (i.e., LG Phillips LP121X1 single CCFL notebookbacklight), and a vertical prism film was placed over the bottomdiffuser (i.e., the lower prism film was oriented with the prismsrunning vertically) while the horizontal prism film was placed over thevertical prism film (i.e., the upper film was placed with prisms runninghorizontally). The inverter was a Taiyo Yuden LS 390 (commerciallyavailable from Taiyo Yuden (U.S.A.) Inc., Schaumburg, Ill.). Athermocouple was used to monitor the temperature of the active backlightin real-time while letting the system equilibrate (until the averagetemperature did not change more than 0.1° F. over a 5 minute duration).Once equilibrium was attained, the Microvision SS220 display analysissystem (commercially available from Microvision, Auburn, Calif.) outputthe luminance in units of candelas per square meter (also known as“nits”). These units were converted to “relative luminance units”compared with a BEF-II film standard (commercially available fromMinnesota Mining and Manufacturing Co., St. Paul, Minn.). It is notedthat the Microvision software included: luminance uniformity—measuredon-axis luminance across 13 points of the backlight; and viewangle—measured luminance as a function of angle at the center point ofthe backlight.

A 3^(rd)-generation electroform designated M-1-1-1 (i.e. the 1^(st)3^(rd)-generation copy of the 1^(st) 2^(nd)-generation copy of the1^(st) 1^(st)-generation copy of the master “M”) was prepared accordingto the process described above to produce 67 4^(th)-generationgeneration copies of itself. Copies number 2 and 67 were used to producedisplay films that were tested for luminance. The films from the 2^(nd)copy had an average normalized luminance of 103.5% with a standarddeviation of 0.19%, while the films from the 67^(th) copy had an averagenormalized luminance of 103.2% with a standard deviation of 0.22%, whichmakes them statistically equal at a 95% confidence limit. In otherwords, even after 67 production cycles, there was no decrease in qualityof the film produced.

The present electroplating process is more effective than prior artprocesses, e.g., the replication accuracy has been maintained forgreater than or equal to about 100 replicas. For example, due to thepassivation process, the replicas (i.e., next generation sub-masters)readily separate from the sub-master after the plating process withoutloss of surface features.

Additionally, the post-treatment process for treating the sub-masterprior to using the sub-master in production of a product (such as adisplay film), enables the reproducible production of a more regulargeometric pattern than when the sub-master has been post-treated withdeionized water and a caustic media (pH of about 8 to about 14). Thispost-treatment, which uses a cathodic current and acidic media, isparticularly useful on electroforms used in the production of articlesfrom a polar material. The caustic media can be employed with theelectroform between product production runs, to reduce, and possiblyeliminate, 7 particulate and staining defects from the microstructuredelectroform surface; resulting in tool yield improvements.

It is noted that the mounting techniques, and/or passivation techniquesdisclosed above can be used with various processes for producing anelectroform (e.g. a sub-master), and are not limited to theelectroplating technique discussed herein. Other possible processes fordepositing the metal material onto the master or sub-master to producethe next generation sub-master include plasma spraying, vapor deposition(e.g., chemical vapor deposition), electroless plating.

As previously noted, the electroforms can be used to produce objectscomprising microstructures with nanoscale resolution, such as films.These films can be used in various applications, e.g., in lightmanagement applications (e.g., as a part of a light management article).For example, the film can be used in to direct, diffuse, and/or polarizelight. The films can be brightness enhancement films used in backlightcomputer displays or other display systems. Some other potentialapplications include graphical applications (e.g., labels, flooringgraphic applications, and so forth), automotive overlays, instrumentclusters, tridimensional molded parts (e.g., with multicolor graphicsthat can be backlit), and so forth. The films can be used alone or inmultilayer structures. For example, in applications such as thosedescribed in U.S. Published Application No. 2004/0228141 A1 to Hay etal.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing fromessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method for making an electroform, comprising: forming a sub-mastercomprising a surface comprising microstructures with nanoscaleresolution; passivating the sub-master to form a passivation layer,wherein passivating comprises contacting at least a surface of thesub-master to be passivated with a solution comprising an oxidizingagent, and applying an anodic current to the sub-master, wherein thesub-master comprises nickel; plating the surface of the sub-master witha metal to form a metal layer; and removing the metal layer to form theelectroform, wherein the electroform comprises the microstructures withnanoscale resolution.
 2. The method of claim 1, wherein themicrostructures comprise a light-reflecting element selected from thegroup consisting of cube-corners, trihedral, hemispheres, prisms,ellipses, tetragonal, grooves, channels, microlenses, and combinationscomprising at least one of the foregoing.
 3. The method of claim 1,wherein the sub-master has no visible damage as determined with a 40×microscope after the production of greater than or equal to about 50electroforms.
 4. The method of claim 3, wherein the sub-master has novisible damage as determined with a 40× microscope after the productionof greater than or equal to about 75 electroforms.
 5. The method ofclaim 1, wherein the solution is an aqueous solution having a pH ofgreater than or equal to about
 10. 6. The method of claim 5, wherein thepH is about 12 to about
 14. 7. The method of claim 1, wherein thesolution further comprises a surfactant.
 8. The method of claim 1,wherein the anodic current is applied at about 1 ASF to about 40 ASF. 9.The method of claim 8, wherein the anodic current is applied at about 5ASF to about 25 ASF.
 10. The method of claim 9, wherein the anodiccurrent is applied at about 5 ASF to about 10 ASF.
 11. The method ofclaim 1, wherein the sub-master comprises a nickel alloy.
 12. The methodof claim 11, wherein the sub-master further comprises cobalt.
 13. Themethod of claim 1, wherein the solution further comprises an alkalimetal hydroxide.
 14. The method of claim 1, wherein the passivationlayer has a thickness of about 10 Å to about 500 Å.
 15. The method ofclaim 14, wherein the thickness is about 15 Å to about 60 Å.
 16. Themethod of claim 1, further comprising rinsing the passivation layer withwater.
 17. The method of claim 1, wherein plating the surface furthercomprises: disposing the surface in an electroforming solutioncomprising a sulfamate, and having a pH of less than or equal to about6; using the sub-master as a cathode; and applying an electroformingcurrent; wherein the electroforming solution and/or an anode comprisethe metal.
 18. The method of claim 17, wherein the metal comprisesnickel and cobalt.
 19. The method of claim 17, wherein theelectroforming current is about 2 ASF to about 100 ASF.
 20. Anelectroform produced by the method of claim
 2. 21. A film formed fromthe electroform of claim
 20. 22. A light management article comprisingthe film of claim
 21. 23. The article of claim 22, wherein the articleis a backlight computer display.
 24. A method for making an electroform,comprising: forming a sub-master comprising microstructures withnanoscale resolution; contacting at least a surface of a sub-master witha solution comprising an alkaline metal hydroxide, wherein the surfacecomprises features to be replicated, and wherein the sub-mastercomprises nickel; applying an anodic current of about 1 ASF to about 40ASF to the sub-master to form a passivation layer having a thickness ofabout 10 Å to about 500 Å; plating the surface of the sub-master with ametal to form a metal layer; and removing the metal layer to form theelectroform, wherein the electroform comprises the microstructures withnanoscale resolution.
 25. The method of claim 24, wherein plating thesurface further comprises: disposing the surface in an electroformingsolution comprising a sulfamate, and having a pH of less than or equalto about 6; using the sub-master as a cathode; and applying a current;wherein the electroforming solution and/or an anode comprise the metal.26. An electroform produced by the method of claim
 24. 27. A film formedfrom the electroform of claim
 26. 28. A light management articlecomprising the film of claim
 27. 29. The article of claim 28, whereinthe article is a backlight computer display.